1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to apparatus and methods of connecting two tubulars. More particularly still, the invention relates to apparatus and methods of connecting two expandable tubulars at the well site.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that moves downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well to a depth whereby the upper portion of the second liner overlaps the lower portion of the first string of casing. The second liner string is then fixed or hung in the wellbore, usually by some mechanical slip mechanism well-known in the art, and cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth.
However, one drawback of this process is that as the wellbore is extended, the inner diameter of the well progressively decreases. This is because subsequent liners must have an outer diameter that is smaller than an inner diameter of earlier casings in order to pass through the earlier casings. As a result, top-hole sizes must be sufficiently large so that the final casing has the desired inner diameter size.
Recently, expandable tubular technology has been developed to overcome this problem. Generally, expandable technology enables a smaller diameter tubular to pass through a larger diameter tubular, and thereafter expanded to a larger diameter. In this respect, expandable technology permits the formation of a tubular string having a substantially constant inner diameter, otherwise known as a monobore. Accordingly, monobore wells have a substantially uniform through-bore from the surface casing to the production zones.
A monobore well features each progressive borehole section being cased without a reduction of casing size. The monobore well offers the advantage of being able to start with a much smaller surface casing but still end up with a desired size of production casing. Further, the monobore well provides a more economical and efficient way of completing a well. Because top-hole sizes are reduced, less drilling fluid is required and fewer cuttings are created for cleanup and disposal. Also, a smaller surface casing size simplifies the wellhead design as well as the blow out protectors and risers. Additionally, running expandable liners instead of long casing strings will result in valuable time savings.
Typically, expandable liners are constructed of multiple tubulars connected end to end. The tubulars are generally connected using a threaded connection. As the threads are made up, a metal-to-metal seal is created between the two tubulars. Thereafter, the entire length of the expandable liner is deployed into the wellbore. The expandable liners are typically expanded by the use of a cone-shaped mandrel or by an expander tool, such as a rotary expander tool having one or more rollers.
A problem arises when the threaded connection is expanded. Generally, the male and female threads of a threaded connection are specifically designed to mate with each other to form a fluid tight seal. However, the specifications of the threads do not take into account the expansion of the threaded connection. By plastically deforming or expanding the threaded connection, the requirements of the threads to form a fluid tight seal are necessarily altered. For example, the tight metal-to-metal seal created between the female thread and the male thread becomes slack, thereby jeopardizing the seal at the threaded connection.
A need, therefore, exists for an expandable tubular connection. There is a further need for a method of forming a tubular connection that maintains a fluid tight seal upon expansion of the tubular connection.